Conventional water heaters include a water storage tank, a cylindrical outer casing concentrically positioned around the water storage tank, and an annular cavity disposed therebetween. Foam insulation is typically injected into the annular cavity to significantly reduce the escapement of thermal energy from the water storage tank to the surrounding environment. A top cover is fastened to the outer casing thereby substantially enclosing the annular cavity.
For example, U.S. Pat. No. 5,023,031 discloses a method of insulating a water heater with an expandable foam insulating material. The foam is injected into the annular space between the water tank and the outer jacket. The foam is injected into a sleeve, which acts to confine the foam during its most liquid state, positioned within this space.
Also, U.S. Pat. No. 4,861,968 discloses a water heater comprising a water tank having a component intended to be kept substantially free from contact with an expandable foam insulating material. The water heater has a jacket surrounding the tank and providing an insulating space therebetween. Positioned within this space is a pair of flexible sheets forming an apron. The sheets are joined to form a seal protecting the components from contact with the foam. The sheets of the apron are substantially unsealed along the top and a side. Foam is introduced between the sheets of the apron and flows out of the unsealed side of the apron to fill the space between the tank and the jacket.
In U.S. Pat. No. 4,808,356, there is disclosed an apparatus and method of insulating a water heater that utilizes a foaming apron comprised of substantially parallel flexible sheets having an open end and open edges. One sheet is attached to the wall of a water tank and the space between the sheets is open to receive one or more charges of foam forming liquid. Preferably one pouring is performed in conjunction with an open centering template, thereby creating a uniform sealing insulation layer around the water tank. After one charge has solidified sufficiently to maintain the jacket properly centered, the centering template may be removed and one or more further charges of foam forming liquids is introduced.
Despite the foregoing improvements, there is a continuing need to further develop methods and apparatus for insulating water heaters.